MMU Nextruder mod tension screws
Goodday,
I installed an MMU3 on my core one.
Since the beginning i have trouble with the tension screws. Somehow the bite/scratch in the aluminum heatbreak.
At first i printed an other screw holder (right after the screwshead) that was shaved off 1 or 1.5mm. Because this holder was rubbing so hard the tensioner would not come back to its original poistion.
I added 0.1mm shims to avoid the heads being pulled in the plastic thingy because of temps. (other problem)
Today i check after a few mmu prints and there is a lot of metal shavings on the heatbreak.
When i undo the tensioner or bolts everything seem to run fine. I always press the bolt when i open tensioner and they seem to move freely.
Now i have altered the bolt threads so they don't act like an jigsay in the holes.
Now it is really smooth but....
this is not normal right??
RE: MMU Nextruder mod tension screws
I would say yes, not normal. I have the CORE One (assembled) with MMU3 (kit) and see no issues like this.
this is not normal right??
RE: MMU Nextruder mod tension screws
Maybe my tensioner arm is too short?
So the bolts are not in line with the holes?
RE: MMU Nextruder mod tension screws
I am sorry, i mean the swivel should be pointing up. Mine is pointing down
RE: MMU Nextruder mod tension screws
It's unclear which metal parts the two tension screws could come into contact with.
In your case, I recommend completely disassembling the Nextruder into its individual parts.
This will also determine which part is causing the metal abrasion.
Then reassemble strictly according to the assembly instructions
https://help.prusa3d.com/de/guide/9d-core-one-nextruder-mod_111779
It's important to use the MMU version of the main plate! (I've made that mistake before, too).
RE:
Yes.
I think i reprint the parts. Maybe there is something dimensional off.
In the idler fs (magnet thing) maybe the screws are to tight together. I have one new from prusa in the packaging which i ordered earlier.
I did not bought this set new in box so maybe the previous guy printed the parts himself.
I have the black mjf mainplate tough.
Anyway. I ordered some m3x50 screws. I will cut them to exact length.
I really dont like threads going in and out off holes all delay long. It is just not right.
I did this mod on the mmu3 tensioner screws to. So the thread are not scraping on the idler body. This way tension is always correct en there is no scraping or binding whatsoever.
I dont modify the original screws btw. I keep the originalsin a seperate printer/mmu bags.
RE: MMU Nextruder mod tension screws
The metal wear can only be explained by the screws rubbing against the heatsink holes.
But there's actually enough play in the screws' holes, unless there's a misalignment.
Can you see from the holes which side the wear is on?
The idler nut is hollow, except for the part into which the screws are screwed.
And the screw guide provides the clearance to the gearbox.
So there's no risk of resistance from those parts.
Did you use the "new" longer screws (M3x35)?
The Mainplate has to lie flat on the heatsink, or is there a small gap between them ?
This mainplate !!!
RE:
I don't know. I use thew MJF printed plated.
The front screw is tilted a little downward.
This is the holes with the idler nut fs in front of it. It seems correct. An new idler nut fs measures exact the same distance and hole places with an caliper.
It seems the front hole is scuffed on the downside right and upside on the left (swivel side)
Because of all this it made this mess in ~1200 toolchanges
I also have an clicking sound. It seems the filament is retracted by the extruder motor then, ratatatatata for 1, 2 second before mmu decides to pull filament out.
Is this value fixed? or is it depending on the idler fs hall sensor? So when filament is unloaded and sensor noticed it the mmu unloads it furter?
I would like to alter this value becasue retraction is way to long now.
Is it somewhere here?:
Seems ok:
OK:
Normal screw guide:
Shaved off screw guide for clearance on top of heatbreak:
Anyway i am gonna place the cut m3x50mm or m3x45mm screws. The unthreaded part is 31 or 27mm. Maybe print an other size screw guid to get exact same length as the m3x35mm's.
So the bolt is round and smooth all the way through the holes. I am not gonna let this eat my heatbreak away.
RE: MMU Nextruder mod tension screws
Here this will solve it. Smooth all the way.
Screws with no threads until idler fs nut
A little bit of adjust room but i have 0.1, 0.2 and 0.3 m3 shims to adjust further.
RE: MMU Nextruder mod tension screws
Well. I now i have a serious problem. For 4 times in a row the filament is wrapped around the extruder.
I have printed a few mmu prints succesefully. But after i made this mod which only make the bolts slider better i got this:
I still find the extruder unloading way to long on change. The filament is already out of the extruder but it is still unloading and ratatatatatatata before the mnu pulss it back.
RE:
Well. I now i have a serious problem.
For 4 times in a row the filament is wrapped around the extruder during unload.
I have printed a few mmu prints succesefully. But after i made this mod which only make the bolts slider better i got this:
I still find the extruder unloading way to long on change. The filament is already out of the extruder but it is still unloading and ratatatatatatata before the mnu pulss it back.
RE: MMU Nextruder mod tension screws
If the filament doesn't retract completely, you probably haven't adjusted the length of the PTFE tube.
Menu:
Hardware - MMU - PTFE Tube (length).... mine is 455 mm.
RE: MMU Nextruder mod tension screws
No thats not the case. Ptfe length is for the rapid inserting and slowly the last 2cm before loading. And i have set it to the corect 390mm for core one enclosed.
This is an unload issue. A lot of people have an issue with it.
During ramming etc and initial unload it unloads to long and eventually nags the tip and curls around.
I asked the question before in this topic. What defines the unload time. Time until the sensor trips? or is it a predefined time with cooling tube length etc in prusaslicer?
I think the filament sensor sees the unload on the late side in the extruder and keeps on unloading for to long. (I have read that the orientation of the 3x1 magnet could help in earlier sensing so maybe i have to turn it around)
Maybe i have to recalibrate the filament sensor again.
With only these modded screws which are really the exact same length as the 35mm ones cannot be the issue.
the only change i made is i printed the screw guide which is original 5mm thick in 4.4mm and added on both side an 0.3mm shim so the screw heads and springs dont sink into it because of heat. Which would result in tension dropping over time.
this makes an total of 5mm again. But i adjusted the tips of the screws to the same length so i had a lot more tension with 5mm screw guide + 2x 0.3mm shims = 0.6mm extra tension added.
Anyway.
before with this little tension there is an ratteling at the filament tip going on for a few seconds.
I hope tensioning will solve earlier filament sensor disengagement.
But on the other side more tension will push the filament more in the extruder gear which could lead to grasping it even more.
I have to know where the mmu unload will start at. Is it fixed extruder unload time. Or filament parking position.
Now it is designed as seems to unload 2 seconds extra to kake sure filament is out. But this causes a lot of this issue and unneccesary debris for everybody.